1. Field of the Invention
The present invention concerns a turbine engine comprising means for controlling the play between the rotor and stator and more particularly between the stator and top of the mobile vanes of the rotor.
2. Background of the Discussion
The regular temperature rises to which a turbine engine is subjected generally provoke heat expansions which are important to control in order to prevent in particular gas leaks occuring between the rotor and structure of the stator which surrounds it, as well as to prevent yield losses resulting from these gas leaks.
Aircraft engines (especially those used for the propulsion of jet planes) need to be able to function in conditions able to vary rapidly. These variations in operating conditions may include racing of the cold rotor, striking of the gas control lever, a racing of the hot rotor or all other operating conditions familiar to operators in this particular field.
It is also necessary to obtain constant play between the ferrule of the stator and the rotor during variable functionings, such as those listed above. In particular, it is important that the radial play between the external ends of the mobile vanes of the rotor and the internal ferrule of the stator bearing the fixed vanes for rectifying the flow of air between the mobile vanes are as constant as possible.
Now, the obtaining of these constant plays is relatively difficult owing to the fact of firstly the expansion and variable mechanical construction of the rotor under the effect of speed variations, and secondly the heat rise between the stator and the rotor due to a significant but essential difference of temperature delays.
Various means exist to limit the consequences of wear of the ferrule of the stator due to an expansion of the mobile vanes exceeding expansion during "normal" functioning. One first method consists of producing the ferrules with a coating of a soft material at the location in front of which the mobile vanes pass. Thus, the possible rubbing of the end of the mobile vanes which could occur during a higher expansion of these vanes would provoke a wear of the coating and a shaping of the stator at this location.
Another method able to obtain a satisfactory result consists of producing the stator in such a way so that it is possible to have gas circulate there, this gas being taken from another part of the engine and having a specific temperature and flowrate which produce at will heating or cooling able to adjust the expansions of the ferrule and thus its play with the mobile vanes.
This communication of air at a variable temperature to the structure of the rectifier support, by virtue of a variation of the expansion and contraction speed of the structure, is able to accomodate various engine operating conditions.
In order to ensure the expansion and contraction of the structure as regards the entire circumference of the housing, the latter is generally formed of a single piece, this therefore concerning a housing with a circumference of 360.degree..
The documents FR-2 683 851, FR-2 516 980 and FR-2 482 661 describe turbine engines whose stators comprise double skin housings extending around rotors over a complete circumference, the heating or cooling air circulating between the two skins of the housing. According to these turbine engines, the ferrule elements (or ferrule sectors) are directly linked to the housing. Also, at the time of expansions or contractions of the housing, the ferrule elements may undergo movements which adversely affect the circularity of the structure.
Finally, so as to maintain perfect circularity of the ferrule elements and ensure an immediate reaction of the structure on expansion and contraction, means are used to adapt the ferrule elements to the housing. GB-2 115 487 describes stator rings dove tail nested in supports. The document FR-2 482 662 describes a segmented stator ring pierced with orifices.
None of these adaptation means ensures a flexible link of the ferrule elements with respect to the housing.